Boosted engines may provide a number of benefits, such as decreased emissions and increased fuel efficiency, when compared to naturally aspirated engines having a similar power output. Furthermore, boosted engines may be lighter than naturally aspirated engines having a similar power output. As a result, vehicle efficiency is increased when engines are boosted by devices, such as turbochargers. Therefore, boosting devices have many benefits and therefore are incorporated into some engine designs to improve performance and fuel economy.
However, turbochargers may experience lag during certain operating conditions, such as tip-in, start-up, etc. The lag decreases the power output of the engine and delays throttle response, impacting vehicle performance and decreasing customer satisfaction. Furthermore, fixed vane turbochargers may only be sized to efficiently operate over limited engine speed and load ranges, thereby decreasing engine operating efficiency in certain areas to provide benefit in other areas. Specifically, some turbochargers may have a threshold speed below which a compressor provides negligible boost to the engine and also a choke flow area where additional flow cannot be achieved through the turbocharger regardless of the work extracted from the turbine. Therefore, when the engine is operated below the threshold speed or above the choke flow region, engine performance may suffer.
U.S. Pat. No. 8,109,091 discloses a variable geometry turbocharger configured to alter the aspect ratio of the turbine based on engine conditions. U.S. Pat. No. 8,109,091 also discloses a control system which uses various modules to determine if the vanes in the turbine are stuck or jammed. The modules take into account only engine speed, engine load, and engine temperature to determine if the vanes are stuck or jammed. However, the Inventors have recognized several drawbacks with the VGT system and control method disclosed in U.S. Pat. No. 8,109,091. For instance, using only engine speed, engine load, and engine temperature to determine vane sticking may not be a sufficiently accurate determination during certain engine operating conditions, permitting vane sticking to go undiagnosed. The control method disclosed in U.S. Pat. No. 8,109,091 only determines the engine is operating in an undesirable range of engine speed, load, and temperature regardless of turbine operation. As a result, the turbine vane mechanism may experience excessive friction, thereby causing corrosion and wear in the turbine that can make it more susceptible to sticking due to other forces acting on the vane mechanism and/or other components. It will be appreciated that using only engine speed, engine load, and engine temperature cannot take into account those noise factors and make an accurate determination on vane sticking Specifically, excessive aerodynamic loads may be exerted on the turbine during certain operating conditions that can cause the turbine response to slow down and become stuck and the problem is not accounted for. Moreover, using only engine speed, engine load, and engine temperature to determine turbine vane degradation may lead to false determinations degradation (e.g., malfunction). As a result, unnecessary actions may be taken to resolve this false positive which may impact vehicle performance, increase emissions, etc.
The Inventors herein have recognized the above issues and developed a method for operating an engine system. The method includes indicating a variable geometry turbine degradation based on a comparison of a modeled set of turbine pressure values and a sensed set of turbine pressure values, each set of turbine pressure values including a pressure value upstream of the turbine and a pressure value downstream of the turbine and the variable geometry turbine positioned downstream of an engine cylinder. In this way, a comparison of modeled pressures across the turbine and sensed pressures across the turbine may be used to determine turbine degradation, thereby increasing the accuracy and speed of this determination. Quick determination of a degradation condition can improve the ability of the mitigation actions to be successful by catching the degradation condition before the aerodynamic forces get even larger, making it harder to correct. Consequently, turbine degradation may be diagnosed over a wider range of engine operating conditions.
Further in some examples the method may additionally include, in response to determining the variable geometry turbine degradation, selecting a turbine degradation mitigation action from a group of turbine degradation mitigation actions based on the comparison of the modeled set of turbine pressure values and the sensed set of turbine pressure values. This selection can be tailored to provide a desired response to alleviate the condition without excessive action that can negatively impact vehicle operation. An example would be if the engine is running at very high speed and load and it is desirable for the condition to be alleviated quickly, an effective turbine mitigation may be activation of a turbine bypass valve to avoid further damage to the engine by over-pressurization. Further in one instance, if an engine were running at lower load with lower pressures, the response could be using a mitigation action that has lesser impact on vehicle operation to alleviate the turbine degradation, but decreases (e.g., limits) adverse effects of the mitigation action.
In this way, an action which mitigates (e.g., substantially eliminates) turbine degradation (e.g., malfunction) during the current operating conditions may be selected to improve turbine operation after turbine degradation is diagnosed. Consequently, turbine operation may be improved and the likelihood of the turbine experiencing excessive pressure conditions is significantly reduced, thereby increasing turbine longevity.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure. Additionally, the above issues have been recognized by the inventors herein, and are not admitted to be known.